Baffle assembly



J. L. VAUGHAN BAFFLE ASSEMBLY Jan.' 9,- 196s 2 Sheets-Sheet l FiledApril 8, 1963 FIQI FIG. 2-

i itl INVENTOR JAMES L VAUGHAN ATTORNEY-Z J. L. VAUGHAN BAFFLE ASSEMBLYJam.l 9, 1968 2 Sheets-Sheet 2 Filed April a, 1965 FIG. 8

FI'G. 7

FIG. 6

FIG. IO

INVENTOR. JAMES L. VAUGHAN .//wh/m, I 2W/Mm FIG. 9

ATTORNEY-S'.

United States Patent 3,362,696 BAFFLE ASSEMBLY .lames L. Vaughan,Summit, NJ., assignor to Separation Processes Corporation, Wilmington,Del., a corporation of Delaware Filed Apr. 8, 1963, Ser. No. 271,220 14Claims. (Cl. 261-114) This invention relates to a method and apparatusfor improving the efficiency of liquid-vapor contact by providingincreased uniformity of liquid-vapor contact and by reducing randommixing of the liquid, and more particularly to a baille assembly usefulin apparatus for separating by liquid-vapor contact the components, orfractions, of a mixture of liquids.

Prior art For mixtures of liquids, such as petroleum, it often isnecessary to separate or fractionate the various cornponents orfractions of the mixture. While this may be accomplished in variousways, most commonly today it iS performed in a fractionating tower orcolumn. Generally, a fractionating tower is a tall, narrow, closed,cylindrical structure through which vapor and liquid streams passcountercurrently in intimate liquid-vapor contact with one another. Asused herein, the term vapor includes gasifled liquid of the liquidmixture, gas injected into the column, if such is used, and any mistentrained in the rising gases, which mist should be minimized as itimpairs the efficiency of the tower. In one form of fractionating tower,horizontal perforated trays or plates, spaced vertically in the column,insure intimate liquid-vapor contact. The input mixture of liquids,which often is preheated, is supplied to the tower at a selected one ofthe perforated trays making up the tower. This input mixture joins thedescending liquid stream from the next higher tray and, as with the restof the trays, the whole of the liquid reaching it flows across the trayas the vapor passes up through the perforations in the tray and throughthe liquid producing an agitated dispersion of vapor and liquid, or whatmay be termed a liquid-vapor foam. The level of liquid on the tray iscontrolled and maintained by a weir over which the outgoing liquid flowsinto a downcomer, or pipe, that feeds the liquid to the next lower tray.

The lighter, more volatile fractions of the liquid mixture will begasied or vaporized by heat provided to the column, generally throughthe provision of a reboiler vaporizing the lower boiling fractions ofthe mixture reaching the bottom of the column, an-d rise throughperforated trays in succession resulting in an increased concentrationof lower boiling fractions in the product flowing as a vapor out the topof the column. After cooling and condensing these overhead vaporfractions, a portion of them are returned to the top tray of the columnto effect countercurrent contact with the rising vapor. The heavierfractions increase in concentration in the liquid as it passes down thecolumn and across each succeeding lower tray as liquid, the lighterfractions being vaporized during this passage. rfhis separation of theliquid mixture into a larger proportion of lower boiling fractions inthe upper portion of the column and higher boiling fractions in thelower portion of the colunm results in a temperature gradient throughoutthe column, the liquid on progressively lower trays being atprogressively higher temperatures.

Briefly, fractionation of the liquid mixture occurs as follows. As theliquid mixture flows across a perforated tray, it will be contacted bythe vapors rising through it from the trays beneath it, which have alarger proportion of the higher boiling fractions. The higher boilingfractions in the vapor will condense and result in the 3,362,696Patented Jan. 9, 1968 vaporization of lower boiling fractions in theliquid. The vapors thus enriched in the lower boiling fractions thenpass to the tray above where the process is repeated. As the vapors risethrough successive trays and Contact the liquid flowing across eachtray, the vapors become increasingly enriched in the lower boilingfractions. At the same time, the liquid flowing down the column becomesincreasingly enriched in the higher boiling fractions. ln this manner,the material fed to the column may be separated into fractions of lowerboiling and higher boiling characteristics.

For best fractionation of the liquid mixture, it is necessary that allthe liquid be distributed at a uniform level about the perforated traywhile the liquid flows in a uniform manner across the perforated area,and that the Vapor rising through both the tray and liquid be uniformlydistributed about the tray and throughout the liquid. lf the liquid isnot distributed at a uniform level about the tray, a greater liquidpressure, or hydraulic resistance, will be encountered by the vaporrising through the tray at the area where the liquid level is greatest.The vapor flow then will naturally tend to be reduced in this area ofincreased resistance, and increased in the area. where the resistanceand liquid level is least. This results in the vapor channeling throughthe column without uniformly contacting the liquid, which reduces thefractionating efficiency of the tray. If therate of liquid ilow acrossthe tray is not uniform, but rather some of the liquid shunts past theperforations around the edge of the tray for example, then liquid maybypass the liquid-vapor contacting operation of the tray, reducing thefractionating efliciency of the tray. Also, it is known that if theliquid can be made to ilow across the tray in a manner such that thereis a minimum of back-mixing of the liquid on the down-stream portions ofthe tray with the liquid on the upstream portions of the tray, theeiiciency of the fractionation operation may be greatly improved, sinceby decreasing such backrnixing there will be a higher averageconcentration of the lower boiling fraction on the tray. If the vapordoes not rise through the tray uniformly distributed about the tray andthroughout the liquid, the liquid will not be uniformly contacted by thevapor and the 4best fractionation of the liquid mixture will not beobtained. In short, for best fractionation efficiency, it is essentialthat the liquid move across the perforated tray with a mini-` dangersand maximize fractionation efliciency. For exam' ple, various types ofperforated tray bubble cap structures have been devised to contrai theflow of vapor through the tray perforations and liquid on the tray.Sorne of these tray structures valso give the vapors a downstreamcomponent, to push at least the liquid adjacent the tray downstream.This is of limited effectiveness in improving the uniformity ofliquid-vapor distribution and does not decrease the back-mixing. Also,baffles have been submerged in the liquid to control and direct liquidilow across the perforated tray. These bailles have permittedback-mixing of the liquid, and increased the hydraulic gradient, therebyimpairing the fractionating efficiency of the tray. Some bales requireimperforate sections on the tray to permit the liquid-vapor foam flowingacross the tray to coalesce.

Besides increasing the hydraulic gradient, this effectively removes asubstantial portion of the perforated area of the tray from theliquid-vapor contacting operation, thereby further reducing thefractionating eiiiciency of the tray. In short, no bubble cap or bafflestructure has yet been de vised which has proven entirely satisfactoryin maximizing the eiiciency of fractionation of the liquid mixture.

The invention rlhe present invention relates to a baflie assembly usefulin a fractionating tower. The baffle assembly has at least two wallelements, a lower wall element which may be attached in a fiuid-tightmanner on the perforated area of a perforated tray, and an upper wallelement, the lower edge of which forms with the upper edge of the lowerwall element a substantially horizontal orifice which, during normaloperation of the tower, is submerged in the liquid on the tray. Thelower wall element extends under the horizontal orifice and preventsvapors issuing from the perforations in the tray from 1passing upwardlythrough the horizontal orifice. Preferably, the upper wall element isslanted in a downstream direction to control and direct, with thehorizontal orifice, the flow of both vapor and liquid. Also the baiileassembly preferably is used with a notched outlet Weir at the downstreamend of the perforated tray which controls the liquid level and backpressure on the tray.

ln this specification, when an element is referred to as slantingupstream or tilted in an upstream direction, it means that the upperedge of the element is horizontally displaced from the vertical planedefined by the lower edge of element in a upstream direction, i.e. adirection opposite to the direction of ilow of liquid across the tray.Similarly, a downstream slant or tilt means that the upper edge of theelement is horizontally displaced from the vertical plane defined by thelower edge of the element in a downstream direction.

The baffle assembly will be further described in connection with theaccompanying drawings, in which:

FIG. 1 is a diagrammatical view of a fractionating tower and itsassociated apparatus;

FIG. 2 is a longitudinal section view of a portion of the ractionatingtower with the outer wall removed and in operation, with baiileassemblies mounted on the per- -forated trays;

FIG. 3 is a transverse sectional view taken on lines 3-3 of FIG. lshowing the bafile assemblies mounted on a perforated tray;

FIG. 4 is an enlarged perspective view of one of the bailie assembliesillustrated in FIG. 2;

FIG. 5 is a perspective view of a notched weir and a section of theadjacent perforated tray;

FIGS. 6 to 10 are vertical, cross-sectional views through modified bafeassemblies; and

FIG. 11 is an enlarged perspective View of another modified bailleassembly.

A typical fractionating tower arrangement minus the bailies of thepresent invention is shown in FIG. 1. The vertical, cylindrical,fractionating tower 1 has a plurality' of horizontal, generally discshaped, perforated trays 2 supported therein in a conventional mannerand across which liquid may flow. A vertical plate 3 is attached to achordal edge of each tray, the lplates on adjacent trays being onopposite sides of the tower. A top portion of plate extends a few inchesabove tray 2, and forms an outlet weir 4, which dams liquid ilow acrossthe tray. The major bottom portion of each plate extends towards thenext lower tray 2, and with the adjacent side of the tower forms adowncomer 5 for disengaging vapor from the liquid-vapor foam andsupplying liquid owing over weir 4 to the next lower tray. The loweredge of plate 3 lies approximately in the plane of the top edge ofoutlet weir 4 of the next lower tray, and during operation of the towerlies within the liquid on the next lower tray to prevent vapor fromchanneling up the downcomer. Each tray has a plurality of small,regularly spaced openings or perforations 6 between the downcomer andoutlet weir through which the vapor rising in the tower may pass tocontact the liquid iiowing across the tray.

The input mixture of liquids 7 is supplied to the tower at a selectedone of the perforated trays. This input mixture joins the descendingliquid stream 8 from the next higher tray and the whole of the liquidflows across the tray, cascading in a zigzag fashion down the tower andacross each tray. As the vapor 9 passes upwardly through the tower, itpasses through the perforations in each tray and through the liquidflowing across each tray, producing on each tray an agitated dispersionof vapor in the liquid, or what may be termed a liquid-vapor foam. Asthe warmer vapor passes upwardly through the cooler liquid, the vaporapproaches an equilibrium with the liquid and, as described before, theless volatile com ponents of the vapor will condense in the liquid,thereby causing the more volatile components of the liquid to vaporizeand rise through the liquid, separating the input mixture of liquid intopredominantly lower boiling fractions at the top of the tower and higherboiling fractions at the bottom of the tower.

The less volatile, or higher boiling fractions 11 of the liquid mixtureare withdrawn from the bottom of the column. One portion 12 of thesefractions is heated by a reboiler 13 and returned to the bottom sectionof the column. The other portion of these heavier fractions 11 arewithdrawn as the heavier boiling fractions product 14. The lighter, moreVolatile components, or lower boiling fractions 15, are withdrawn asvapor from the top of the column and supplied to a condensor 16. Afterthese overhead vapor fractions are cooled and condensed by thecondenser, one portion 17 of them is returned to the top tray of thecolumn to cascade as liquid in a zigzag fashion down the column andacross each perforated tray. The other portion 18 of them is withdrawnas the lighter boiling fractions product. The structure and operation sofar described is well known to those skilled in the art.

An inlet Weir 19 is attached to each perforated tray 2 beneath andslightly downstream of the downcomer S, and preferably at the upstreammargin of the perforated area of the tray. The inlet weir inhibits thefree flow of liquid from the downcomer across the perforated area of thetray by damming the flow of incoming liquid from the downcomer at alevel adjacent to the tray to form a pool of liquid between the inletWeir and the side of the tower. This pool of liquid inhibits channelingof vapor through the downcomer at low liquid ilow rates. At high liquidflow rates, the inlet weir 19 also causes the incom ing high velocityliquid to iiow onto the perforated area of the tray at a levelsubstantially above the perforated tray and with a substantiallyincreased horizontal velocity component thereby decreasing the tendencyof this high velocity liquid stream to reduce the vapor ow through theinitial rows of -perforations in the tray and to flow through theseperforations, bypassing the contacting operation. Thus, the inlet Weiralso eifcctively decreases weeping of the liquid through the adjacentfirst -few rows of perforations in the perforated tray at high liquidrates.

Preferably a plurality of baiile assemblies 21 are mounted within theperforated area of each perforated plate 2 spaced downstream one fromthe other, as shown in FIG. 3, the baiile assembly furthest upstreambeing spaced downstream xfrom the inlet weir. For normal ow rates, thebaie assemblies may be spaced about 6 inches to 4 feet apart, dependingupon the liquid :llow rates. As shown in FIGS. 2-4, each bale assemblyincludes a lower flange 22 having openings 23. Bolts 24 pass throughopenings 23 and through perforations in the perforated tray 2, and a nut2S is threaded tightly on to the free end of the bolt lbeneath theperforated tray, the nuts and bolts clamping the bale assemblies to theperforated tray in a fluid-tight manner. While it is preferred to usebolts to attach each baffle assembly to the perforated tray, the

baffle assemblies may be attached in a iluid-tight manner to theperforated tray in various other ways, such as by weldin-g flange 22 tothe perforated tray. Each baille assembly includes a lower wall 26 andan upper wall 27. 'I'he lower wall 26 extends upwardly into the lowerlevel of liquid ilow across the tray from one end of flange 22, andpreferably is tilted in an upstream direction. The upper wall 27preferably is attached to the lower Wall and flange 22 by legs 28extending from the lower edge of the upper wall to the iiange, and webs29 are provided between the sides of legs 2S and the adjacent sides ofwalls 26 to prevent iluid ilow therethrough. The upper wall lies in anupper level of liquid ilow across the tray, and preferably is tilted ina downstream direction. The lower edge 31 of the upper wall is spaceddownstream from the upper edge 32 of lower wall 26, the edges preferablylying substantially in a horizontal plane and providing a horizontalorifice 33 therebetween. The horizontal orifice should not be higherthan the top of the outlet weir, for free ilow of foam therethrough, andmay be somewhat lower than the top of the outlet Weir. Each bailleassembly may be pressed or otherwise formed a single sheet of metal, thelegs 28 of the upper wall thus lying between the adjacent edges of thelower wall sections 26.

Preferably, the baille assemblies are of standard lengths, or of thesame length, alternate ends of the baille assemblies abutting againstopposite sides of the fractionating tower as illustrated in FIG. 3. Thisarrangement prevents liquid from flowing past the ends of the bailleassemblies and shunting around the perforations and along theimperforate margin of the tray to the outlet weir 4. Rather, allincoming liquid must ilow past at least one baille assembly and acrossthe perforated portion of the tray, the baille assembly therebycontrolling the velocity and movement of the liquid across theperforated tray. At low liquid and vapor ilow rates, such as areencountered during start-up of the fractionatin-g tower, while the vaporilow rates might not be sufiicient to cause the foam to ilow over theupper edge of lower wall 26 of the baille assembly to establish auniform liquid level on the tray without weeping, still the liquid mayilow in a zigzag fashion around the end of each baille assembly which isspaced from the side of the fractionating tower, and past each bailleassembly across the portion of the perforated tray between the bailleassemblies to the outlet weir 4, as indicated by arrows 34. Thus, bythis arrangement of the baille assemblies, uniform conditions ofliquid-Vapor Contact may be established even at low Vapor ilow rates.

Operation As the vapor bubbles through the liquid on the perforatedtray, the rising bubbles in the liquid push ahead of them a substantialamount of liquid, the liquid adjacent the bubbles flowing around theside of the bubble and back over the bubble, producing in the path ofthe bubble a generally upward flowing stream of liquid. As the rate ofvapor ilow rises, more and more bubbles pass through the liquidproducing a greater upward ilow of the liquid, as indicated by theincreasing height of the foam surface above the tray with increasingvapor ilow rates. For any segment of the foam, the vapor bubbles passingthrough the segment produce an upward force counterbalanced and offsetby the downward gravitational .force of the liquid.

The lower wall 26, extends under and completely across the vertical zonedefined by the horizontal orifice 33. Thus, the vapor bubbles issuingfrom the perforations in the vertical zone beneath the horizontalorifice and lower wall 26 are deflected in an upstream direction by thelower wall, sweeping with them the liquid beneath the lower wall andproducing a strong upward ilow of bubbles and liquid adjacent the upperedge 32 of the wall. Since the vapor issuing from the perforated tray isdeilected away from the zone vertically above the horizontal orifice bywalls 26 and 27, the upward current of liquid and vapor in this zone isappreciably reduced with respect to the upward ilow of liquid adjacentand upstream of this zone. The liquid in a segment of liquid-vapor foamabove the perforated tray -which flows downstream into this zone willhave a given amount of lpotential energy with respect to the tray,depending on its height above the tray. Since the velocity of upwardilow of liquid and vapor vertically above the horizontal orifice 33 isappreciably reduced, the liquid flowing into this zone will tend tofall. The potential energy of the liquid flowing into the zone isconverted to kinetic energy as the liquid drops through this zone andthrough horizontal orifice 33. The upper sunface of lower wall 26directs this downwardly ilowing mass of liquid carrying entrained vaporwith it downstream in a generally horizontal direction, turning thedownward force of kinetic energy outwardly and horizontally in adownstream direction.

Lower Wall 26, by being attached in a iluid-tight manner to theperforated tray, prevents leakage of iluid from one side of the bailleto the other side of the baille. Because the lower wall and 4perforatedtray in this manner effectively isolate the iluid pressures upstream anddownstream of the baille assembly from one another, it is possible tohave a different liquid and vapor pressure downstream of the bailleassembly than upstream of the baille assembly adjacent lower wall 26.And because of the appreciable kinetic ener-gy of the liquid and Vaporflowing through the horizontal orice, the pressure downstream of thebaille assembly actually may Ibe greater than the pressure upstream ofthe baflle assembly. Thus, by using only the horizontal orifice formedby the two walls, and yby attaching the lower wall to the perforatedtray in a iluid-tight manner, it is possible to have an equal, lesser,or even greater pressure and height of liquid and vapor downstream ofthe baille assembly than upstream of the baille assembly. By varying thesize of the horizontal orifice, the resistance to the ilow of liquid andvapor through the horizontal orifice may be varied.

Because of these two factors-the horizontal orifice and the isolation ofpressures-it is possible by selecting the appropriate size orifice topresent just enough resistance to the ilow of liquid through thehorizontal orifice to make the downstream pressure equal to the upstreampressure. Accordingly, the downstream liquid and vapor level will beexactly equal to the upstream liquid and rvapor level, and the desiredzero hydraulic gradient across the plate as a whole results.

The resistance to ilow of liquid and vapor through any given size ofhorizontal orifice also effectively may be varied by varying the planeof the orifice from the horizontal. In other words, by making the loweredge 31 of upper wall 27 higher than the upper edge 32 of lower wall 26,effectively opening the orifice, some leakage of the increaseddownstream pressure back through the horizontal oriiice to the upstreamside of the baille assembly is permitted, reducing the downstreampressure. By forming the baille assembly with lower edge 31 of upperWall 27 lower than the upper edge 32 of lower wall 26, effectivelyclosing the oriiice, ilow of liquid and vapor through the orifice willbe further restricted by the slight channel between the two walls, andthis added restriction will decrease the kinetic energy of the liquidand vapor flowing through the orifice, reducing the downstream pressure.Preferably though, ilow through the oriiice is not restricted for thisjust absorbs energy, and the adjacent edges of the walls lie either in ahorizontal plane, or the lower edge of upper wall 27 is slightly higherthan the upper edge of lower wall 26.

lf only lower wall 26 of the baille assembly were provided, it wouldserve as an obstruction to the ilow of foam across the perforated tray,thereby resulting in excessive resistance to ilow and a high hydraulicgradient which would yield a poor vapor-liquid distribution about thetray. lf only upper wall 27 were provided, again an obstruction to theilow of liquid across the tray would be provided, resulting in highresistance to the flow of liquid across the tray. Because of theobstruction encountered if either lower wall 26, or upper wall 27 wereprovided, an appreciable hydraulic gradient would result. In short, ifeither wall 26 or wall 27 were used alone, fractionating efficiency ofthe tray would be reduced. If walls 26 and 27 were combined to provide abafiie assembly such as that just disclosed, but foam was permitted toflow back under or through the baffle assembly, such as would occur ifthe lower wall of the baic assembly were spaced from the perforatedtray, or openings were provided through the lower wall, then thepressure differential advantage available from the baflie assembly wouldbe negated. This arrangement too, then, would only restrict the fiow ofliquid across the perforated tray and impair the fractionatingefficiency of the tray. For a pressure differential advantage to beprovided by the baie assembly, it is necessary for the lower wall of thebathe assembly and the adjacent supporting flange to be connected to theperforated tray in a Huid-tight manner, thereby maintaining the pressuredifferential across the bathe assembly adjacent the perforated tray.

For normal flow rates, the area of this generally horizontal orifice 33may be about one-quarter or less of the cross-sectional area of theliquid-vapor foam adjacent the bafe assembly at generally used liquidand vapor rates. That is, for an orifice which extends completely acrossthe liquid and Vapor stream, if the upper surface of the -foam were 6inches above the surface of the perforated tray, then the width of theorifice would be about 11/2 inches. This relationship will provide, orclosely approximate, a zero hydraulic gradient at generally used liquidand vapor rates.

Placing a horizontal orifice in the liquid may be compared to placing adisc in the path of iiuid ow through a pipe, the disc having a smallopening therethrough. As is well known, for fluid flow through this.`pipe, the opening through the disc would cause a substantial pressuredrop as the fiuid fiowed past the orifice. As the fluid flow increased,this pressure difference also would increase. Such would appear to bethe case if a bafie having a horizontal orifice were placed in the pathof liquidvapor iiow across a perforated tray. The downstream vpressurewould seem to be substantially less than the upstream pressure, and asubstantial hydraulic gradient necessarily would seem to result.However, such is not the case. By providing an appropriate baffle, suchas that just described, not only is the downstream pressure notsubstantially less than the upstream pressure, but rather it may be madeequal to, or even greater than, the upstream pressure by appropriatecorrelation of variables, such as liquid and vapor ow rates and orificesize.

As the liquid and vapor stream issues from the orifice and movesdownstream of lower wall` 26, the vapor bubbles rising from theperforations immediately downstream of ange 22 provide a lifting effect,carrying the liquid up. As these vapor bubbles engage the lowerdownstream surface of upper wall 27, they are defiected in a downstreamdirection by this surface. As the bubbles rise along this surface, theypush liquid and vapor in front of them, and impart a positive, forward,downstream force to the liquid and vapor. By varying the downstreaminclination of upper wall Z7, the downstream force imparted in theliquid and vapor by upper wall 27 may be varied. Preferably, thedownstream inclination of upper wall 27 is approximately 30 to thevertical. For angles substantially less than this, the downstream forceimparted to the liquid and vapor is decreased to a significant extentand the quality of liquid which may be processed under given conditionsof vapor flow and liquid level is reduced. For angles substantiallygreater than 30, the amount of vapor rising along the lower surface ofupper wall 27 will increase until the liquid and vapor rising along thewall shoots and spits into the vapor area above the surface of the foam.This tends to increase the entrainment of liquid mist in the vaporrising to the next perforated tray, which decreases fractionatingefficiency. Accordingly, a downstream inclination of upper wall 27 ofapproximately 30 is preferred, as it provides a desirable balancebetween the downstream force imparted by the inclined upper wall to theliquid and vapor downstream of the wall, and the entrainment of mist inthe vapor above the surface of the foam.

Specific examples A haffie system, similar to that shown on a perforatedtray in FIG. 2, was constructed and tested. The tray was perforated with1/4 inch openings spaced on @a inch equilateral triangles, a perforationdensity of about 280 openings per square foot. The perforated area ofthe tray was about six feet long and one foot wide. Inlet and outletimperforate calming areas also were provided, each of about two feet inlength. At the end of the calming area, an outlet weir was providedwhich was about 3 inches high. Four bafiie assemblies were mounted alongthe perforated area of the tray, at distances of 2, 3 4 and 5 feet fromthe upstream margin between the inlet calming area and the perforatearea, and each extended transversely completely across the perforatedtray. The lower baffle wall of each baffle assembly' was about 2% incheswide, and tilted upstream at an angle of about 35 to the vertical. Theupper baie wall was about 6 inches wide, and tilted downstream at anangle of about 30 to the vertical. The lower edge of the lower bafflewall was positioned about 3,41 of an inch in front of the vertical planedefined by the lower edge of the upper bafiie wall, and a horizontalfiange about 3A of an inch wide extended from the lower edge of thelower baffle wall under the remaining portion of the vertical zonedefined by the horizontal orifice, completely blocking gas flow from theperforated tray upwardly through the horizontal orifice. The bafiiewalls were mounted on the perforated tray to form a substantiallyhorizontal orice between their adjacent edges of about 2 inches inwidth, the orifice being about 2 inches above the tray. The top of theupper bafiie wall was about 7%r inches above the tray.

The baffle system was tested using water as the liquid and air as thevapor. At a liquid flow rate of 52 gallons per minute, and a vapor flowrate of 1620 cubic feet per minute, the height of the waterair foam wasabout 8 inches above the tray. Since the foam tiowing into the verticalzone defined by the two baflie walls drops as it fiows across and downthrough the zone to the horizontal orifice, and since the foam isejected in a downstream direction adjacent the upper edge of theinclined upper bafiie wall, while the average foam height was greaterthan the height of the baffle assemblies, little or no foam spilled overthe top edge of the upper baflie wall. The height of the foam, and theheight of the liquid on the calming areas, was essentially even acrossthe perforated area of the tray, showing that a zero hydraulic gradienthad been obtained. F or a given Weir height, at s-ubstantially higherfiow rates, the downstream foam level tended to be higher than theupstream foam level, while at substantially lower rates the upstreamfoam level tended to be higher than the downstream foam level. Streamsof dye were introduced in the liquid at the inlet side of the tray, andvisually illustrated the uniform liquid fiow forward through the orificeand across the perforated tray, with little back-mixing even though theheight of the foam was above the top of the baffle assembly.

For the baffle assembiy just described, a substantial variation in flowrates will produce a substantial hydraulic gradient. In other words, azero hydraulic gradient will be obtained with the baffle assembly justdescribed only over a relatively narrow range of fiow rates. In manyfractionating towers, the flow ratesmay vary over a relatively widerange. Thus, it is preferable to provide an assembly which would effecta zero hydraulic gradient over a wide range of fiow rates.

A zero hydraulic gradient may be obtained over such a wide range of flowrates by utilizing, in combination with the baille assemblies, a notchedoutlet Weir 4', such as is shown in FIG. 5. The notched outlet weir willregulate the downstream foam pressure of the baille assembly and therebycounterbalance, for varying flow rates, the correspondingly varyingkinetic energy of the foam flowing through the horizontal orifice anddownstream of each baille assembly. Thus, by providing an appropriatelydesigned notched outlet Weir, the increased kinetic energy of the foamissuing from the baflle assembly as the liquid flow rate and height ofthe foam increases may be exactly offset by the increased back pressureprovided by the notched outlet weir to result in a zero hydraulicgradient over a wide range of flow rates. While a rectangularly shapednotch has been illustrated, other shapes of notches may be provided inthe outlet Weir, depending upon the back-pressure characteristicsdesired.

A baille system simialr to that described in the previous example wasutilized to demonstrate the effect of a notched outlet weir. The upperwall of each of these baille assemblies was angled approxidately 20downstream, rather than 30 degrees as in the previous example, giving atotal baille assembly height of approximately 7%! inches. The perforatedarea of the tray was about lOl/2 inches wide, rather than -one footwide. The notched outlet weir was placed at the downstream end of theperforated area of the tray. The notched outlet Weir was about l()inches in overall height, and a notch of about 4%" wide and 71,3/16inches deep was provided in the top edge of the outlet weir centeredbetween the sides of the weir. The base of the notch was about 23/16inches above the perforated tray. Other than for these differences, theassembly was the same as that described in the previous example.

This assembly was tested using Water as the liquid and air as the Vapor.The vapor flow rate was maintained at 1,458 cubic feet per minute. Afterstartup, for liquid flow rates of between substantially zero and 52gallons per minute, a hydraulic gradient of less than 1A; of an inch wasobtained. This is substantially a zero hydraulic gradient. For a liquidflow rate of 30 gallons per minute, the foam height was approximately 7inches above the perforated tray. For a liquid flow rate of 52 gallonsper minute, the foam height was approximately 81/2 inches above thetray. Again, because the foam drops between the baille walls and intothe horizontal orifice, and because the foam is ejected from the upperbaflle -wall in a downstream direction, little foam spilled over the topedge of the upper wall of the baille assembly. At this gas rate, thesystem was stable at all liquid flow rates up to about 60 gallons perminute. Thus, by utilizing a notched weir it is possible to obtain azero hydraulic gradient over a wide range of liquid ilow rates.

For high liquid flow rates, the baille assembly 4t) preferably includes(as shown in FIG. 6) a lower L-shaped ange 41, a lower wall 42 attachedto the upper end of the L-shaped flange, and an upper wall 43 havinglegs 44 extending from its lower edge and attaching it to flange 41.Webs 45 extend from the sides of the legs to the adjacent sides of lowerwall 42. As with baille assembly 21, preferably this baille assembly ispressed from a single sheet of metal. Lower wall 42 preferably iscurved, the center of curvature being the lower edge of wall 43. By thisarrangement, the size of the horizontal orifice 46 between the adjacentedges of the two walls determines the restriction to the flow of fluidbetween the upper surface of the lower wall 42 and the lower edge ofupper wall 43. That is, the upper surface of lower wall 42 is alwaysspaced from the lower edge of upper wall 43 a distance at least equal tothe width of the horizontal orifice, and no further substantialrestriction is presented to the tlow of iluid between the lower wall 42and the upper wall 43 than is presented by the horizontal orifice. Forhigh liquid ilow rates, the kinetic energy of the liquid flowing throughthe horizontal orifice and dellected in a substantially horizontaldownstream direction by lower wall 42 would, if ejected from the lowerwall adjacent the perforated tray, tend to displace the ilow of vaporthrough the adjacent downstream perforations to the downstream side ofeach perforation, and liquid would tend to weep through the upstreamside of these perforations at low vapor rates. By using an L-shapedflange 41 which spaces lower wall 42 a substantial distance above theperforated tray, liquid and Vapor are caused to issue from the bailleassembly a substantial distance above the perforated tray, therebyminimizing and effectively preventing weeping at high liquid ilow rates.Accordingly, this baille assembly is preferred for high liquid ilowrates.

Should a large variation in flow rates be expected in the fractionatingtower, causing the foam height to vary substantially and possibly wellabove the upper edge of upper wall 27 shown in FIG. 4, the bailleassembly may be modified to include a top wall 47 above upper wall 27',as shown in FIG. 7. Top wall 47 is attached to and spaced from upperwall 27' by legs 48, similar to legs 28 of the upper wall. The loweredge of top wall 47 preferably is as high as, or slightly higher than,the upper edge of wall 27', to provide a second horizontal oritlce 49.Preferably top `wall 47 is angled in an upstream direction. When thelevel of liquid and foam rises above upper wall 27', foam downstream o-fupper wall 27 will tend to spill over the top edge of wall 27 throughorifice 49 and be drawn down through orice 33 with the liquid flowingfrom upstream of the baffle assembly down through the orifice. Thus,back-mixing of the liquids is minimized. However, normally it ispreferred to provide an upper wall 27 of sufficient height so that, atmost, only small amounts of foam downstream of the upper wall will spillback over the upper edge of the Wall.

The lower wall of the baille assembly may be vertical, as indicated bythe baille assembly shown in FIG. 8. For this construction of the bailleassembly, the foam flowing downwardly through the horizontal orifice 33will be directed outwardly, mainly by flange 22, lower wall 26 merelyproviding the horizontal orifice.

Since a substantially vertical upper wall would impart little if anyforce to the foam tending to push it downstream, should it be desired touse a substantially vertical upper wall, a plurality of horizontalorifices may be employed to increase the downstream force imparted tothe foam, as indicated by the baffle assembly shown in FIG. 9. Aplurality of horizontal orifices staggered in a vertical direction alsomay be provided when the upper walls are tilted in a down-streamdirection, as illustrated in FIG. 10.

Rather than providing a baille assembly having long, narrow, rectangularorifices such as are illustrated in FG. 3, the bale assembly may beformed with a number of short orifices as illustrated in FIG. 1l toprovide a baille assembly similar in appearance to a food greater. Suchbaille assemblies may include horizontal orifices quite close to thelower edge of the baille assembly and thus quite close to the perforatedtray, when a minimum liquid level on the perforated tray is desired,such as in cryogenic columns.

While the baille assembly has been described with respect to afractionating tower, it should be understood that it may be incorporatedwith other structures, such as a unit having a iluidized or aerated bedof solid particles, to control the flow of aerated fluids, particularlywhere a downstream pressure equal to or greater than the upstreampressure adjacent the baille assembly is desired.

It is to be understood that various changes may be made in the detailsof the baffle assemblies herein described without departing from theinvention, the scope of the invention being set forth in the appendedclaims.

I claim:

1. For use in vertical fractionating tower having a plurality ofperforated, superposed, spaced horizontal trays each arranged to receivea descending flow of liquid at one side thereof and to carry said liquidhorizontally across said perforated tray to an outlet Weir at the otherside thereof while subjecting said liquid to a vapor stream ascendingthrough the perforations in said trays, a generally vertically-extendingbaffle assembly providing a substantially horizontal orifice forcontrolling the liow of liquid across said trays comprising at least twowail elements extending generally in the same lateral direction andspaced both horizontally and vertically apart, the upper edge of thelower wall element defining the upstream edge of the horizontal orifice,the lower wall element extending only down from the horizontal orifice,the lower wall element being impervious and adapted to be attached tosaid tray in a fluid-tight manner, the lower edge of the upper wallelement defining the downstream edge of the horizontal orifice, theupper wall element extending only up from the horizontal orifice, andthe lower wall element extending under and across the vertical zonedefined by the horizontal orifice.

2. A bafiie assembly as set forth in claim 1 in which the lower wallelement is spaced from the lower edge of the upper wall element adistance at least equal to the width of the horizontal orifice.

3. A baie assembly as set forth in claim 2 in which the upper wallelement is adapted to extend a substantial distance above the top edgeof the outlet Weir, and in which said horizontal orifice defined by theadjacent edges of the said two wall elements is adapted to lie at alevel no higher than the top edge of said Weir.

4. A baffle assembly as set forth in claim 3 in which said top wallelement is tilted in a downstream direction.

5. In a liquid-vapor contact system including a uniformly perforatedhorizontal tray across which liquid may ow and through the perforationsof which vapor may issue to produce a liquid-vapor foam, an outlet weirat the downstream end of said tray, said outlet Weir extendingvertically above the level of said tray and attached to the tray in afluid-tight manner thereby to dam the flow of liquid across the tray andproduce a pool of the liquid-vapor foam on the tray, the improvementcomprising a lower wall extending laterally across the liquid liow,means to attach the lower wall in a duid-tight manner on the perforatedarea of said tray, the upper edge of said outlet weir being at least ashigh as the upper edge of said lower wall, an upper Wall extendinglaterally across the liquid liow, means attaching said upper wall tosaid lower wall over the perforated tray downstream and above the lowerwall with the lower edge of said upper wall in substantially the samehorizontal plane as the upper edge of said lower wall to provide agenerally horizontal orifice between said adjacent edges which extendslaterally across the liquid flow and through which said liquid-vaporfoam may cascade, the height of said lower wall being at least as greatas the width of said horizontal orifice as determined by the spacingbetween said adjacent edges, said lower wall extending under and acrossthe vertical zone defined by the horizontal orifice, said lower wallelement being spaced from the lower edge of the upper wall element adistance at least equal to the width of the horizontal orifice, saidlower and upper walls comprising a baffle assembly.

6. A liquid-vapor contact system as set forth in claim 5 in which aplurality of said baffle assemblies are mounted on said perforated areaof the tray intermediate the margins of the perforated area of the trayand spaced from one another.

7. A liquid-vapor contact system as set forth in claim 5 in which atleast one of said wall elements of the baffle assembly is tilted fromthe vertical by transverse horizonal displacement of that one of itshorizontal edges not defining the horizontal orifice in a downstreamdirection.

8. A liquid-vapor contact .system comprising a perforated horizontaltray for receiving a fiow of liquid thereacross and a flow of vaporthrough the perforations therein, the vapor agitating the liquid andproducing a liquid-vapor foam over the perforated tray, and a generallyvertically-extending battle assembly providing a substantiallyhorizontal orifice, said baffle assembly comprising at least two wallelements' extending laterally across the ow of liquid and spaced bothhorizontally and vertically apart, the upper edge of the lower wallelement defining the upstream edge of the horizontal orifice, the lowerwall element extending only down from the horizontal orifice, the loweredge of the upper wall element defining the downstream edge of thehorizontal orifice, the upper wall element extending only up from thehorizontal orifice, the lower wall element extending under and acrossthe vertical zone defined by said horizontal orifice, and means forpreventing the flow of liquid in an upstream direction under thehorizontal orifice of the bafiie assembly.

9. A liquid-vapor contact system as set forth in claim 8 in which thelower wall element is spaced from the lower edge of the upper walleiement a distance at least equal to the width of the horizontal ororifice as defined by the adjacent edges of said wall element.

10. A liquid-vapor contact system as set forth in claim 9 in which saidmeans for ypreventing the flow of liquid in an upstream direction undersaid horizontal orifice includes a fiange attached to the lower edgeportion of said lower wall element, said ange including a horizontalextending portion, and means to attach the horizontally extendingportion of said liange to the perforated tray in a duid-tight manner.

11. A liquid-vapor contact system as set forth in claim 10 in which theupper wall element is tilted in a downstream direction.

12. A liquid-vapor contact system as set forth in claim 3 including anoutlet weir at the downstream end of said perforated tray, said outletWeir extending vertically above the level of said tray and attached tothe tray in a fluidtight manner thereby to dam the ow of liquid acrossthe tray and produce a pool of liquid-vapor foam on the tray.

13. A liquid-vapor contact system as set forth in claim 12 in which theoutlet weir is notched.

14. A liquid-vapor contact system as set forth in claim 13 in which theupper portion of the outlet weir is notched.

References Cited UNITED STATES PATENTS 180,901 8/1876 Maynard 261-114243,297 6/1881 Perin 261-114 1,893,906 1/1933 Primrose et al. 261-114 XR2,401,569 /1946 Koch 261-114 2,510,590 6/1950 Kraft 261-114 2,693,35011/1954 Ragatz 202-158 XR 2,702,434 2/ 1955 Richardson et al. 2,757,9158/1956 Huggins 261--114 2,832,578 4/1958 Gilmore 261-114 2,926,754 3/1960 Ragatz 261-114 XR HARRY B. THORNTON, Primary Examiner.

RONALD R. WEAVER, Examiner.

E. H. RENNER, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,362,696 January 9, 1968 James L. Vaughan It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 2, line 59, for "central" read Control column 3, line 65, after"plate" insert 3 column 7, line 64, for "in" read to line 69, for"quality" read quantity column l2, line 28, strike out "or".

Signed and sealed this 29th day of April 1969.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

1. FOR USE IN VERTICAL FRACTIONATING TOWER HAVING AA PLURALITY OFPERFORATED, SUPERPOSED, SPACED HORIZONTAL TRAYS EACH ARRANGED TO RECEIVEA DESCENDING FLOW OF LIQUID AT ONE SIDE THEREOF AND TO CARRY SAID LIQUIDHORIZONTALLY ACROSS SAID PERFORATED TRAY TO AN OUTLET WEIR AT THE OTHERSIDE THEREOF WHILE SUBJECTING SAID LIQUID TO A VAPOR STREAM ASCENDINGTHROUGH THE PERFORATIONS IN SAID TRAYS, A GENERALLY VERTICALLY-EXTENDINGBAFFLE ASSEMBLY PROVIDING A SUBSTANTIALLY HORIZONTAL ORIFICE FORCONTROLLING THE FLOW OF LIQUID ACROSS SAID TRAYS COMPRISING AT LEAST TWOWALL ELEMENTS EXTENDING GENERALLY IN THE SAME LATERAL DIRECTION ANDSPACED BOTH HORIZONTALLY AND VERTICALLY APART, THE UPPER EDGE OF THELOWER WALL ELEMENT DEFINING THE UPSTREAMM EDGE OF THE HORIZONTALORIFICE, THE LOWER WALL ELEMENT EXTENDING ONLY DOWN FROM THE HORIZONTALORIFICE, THE LOWER WALL ELEMENT BEING IMPERVIOUS AND ADAPTED TO BEATTACHED TO SAID TRAY IN A FLUID-TIGHT MANNER, THE LOWER EDGE OF THEUPPER WALL ELEMENT DEFINING THE DOWNSTREAM EDGE OF THE HORIZONTALORIFICE, THE UPPER WALL ELEMENT EXTENDING ONLY UP FROM THE HORIZONTALORIFICE, AND THE LOWER WALL ELEMENT EXTENDING UNDER AND ACROSS THEVERTICAL ZONE DEFINED BY THE HORIZONTAL ORIFICE.